There is known from Japanese Patent Application Laid-open No. 2001-132444 an arrangement in which an exhaust port communicating with a combustion chamber of an internal combustion engine is formed from a pipe-shaped member, and by supporting this exhaust port within a cylinder head via a heat insulating layer, it is made difficult for exhaust gas heat to be transferred from the exhaust port to the cylinder head, thus maintaining the exhaust gas at as high a temperature as possible and thereby promoting the warm-up of the internal combustion engine and the early activation of an exhaust gas purification catalyst.
However, in order to recover as much as possible of the waste heat of the internal combustion engine as high temperature steam, it is not enough only to make an evaporator provided in an exhaust passage exhibit its performance effectively by maintaining the temperature of the exhaust gas at a high temperature; it is also necessary to recover heat transferred from the exhaust port to the cylinder head and dissipated to the atmosphere. It is therefore necessary to absorb effectively the heat transferred from the exhaust port to the cylinder head with water flowing through a water passage formed around the exhaust port, thus increasing the temperature of the water as much as possible.